Conventional diesel engines include an exhaust gas purification device arranged in the exhaust passage. The exhaust gas purification device includes a diesel particulate filter (DPF), which captures particulates contained in an exhaust gas, and an oxidation catalyst. Such an exhaust gas purification device treats an exhaust gas to raise the temperature in order to maintain the function of purifying an exhaust gas. The treatment regenerates the DPF by burning the particulates captured by the DPF and activates the oxidation catalyst. A burner that performs the treatment for raising the temperature of the exhaust gas is arranged upstream of the DPF and the oxidation catalyst.
One example of the structure of the burner is a multilayer tube structure. In the multilayer tube structure, a plurality of tubular members is overlapped to be coaxial. For example, Patent Document 1 discloses a combustor including a combustion tube, in which a flame is generated. The combustion tube includes an inner tube and an outer tube. An auxiliary combustion tube is arranged radially inside of the inner tube. The inner tube and the outer tube are fixed to a base. Fuel injected into the auxiliary combustion tube is mixed and evaporated in a premixing region. A flame occurs in a combustion chamber by igniting a premixed air-fuel mixture. Combustion is promoted by supplying air for combustion through combustion holes of the outer tube.